The Development Of Welding Material For ULCB Steel And The Microstructure And Mechanical Properties Of Welded Joint

Most energy field is mainly distributed in the remote areas,such as the desert,landslide,earthquake,ocean,which are required for reliability and security of steel.The polyphase ULCB steels are satisfied the requirements for high toughness and strength,so it is widespread attention by people.For low carbon bainitic steel and the weldability,the research has achieved preliminary results,but the corresponding welding material is rarely researched,and the strengthening and toughening mechanism is not perfect for the weld seam and base metal.The property of the weld seam and base metal is not matching,which leads to the deterioration.Therefore,the research of welding material for the ULCB steel and the strength-toughness mechanism of welded joint are very important.In this paper,ULCB steel was the base metal,combined with software,the ULCB flux was researched by orthogonal design.And ULCB wire was designed by the Mn-Ni-Mo-Re-B alloy system.The experiment was carried out using the United States Lincoln twin-wire welding machine.The microstructure and properties of ULCB steel welded joints were studied under different welding heat input,and mathematical models of tensile strength and impact energy were established by software.The results showed that the optimum conditions are as follows:the content of A1203 is 10%,Ti02 of 6%,Zr02 of 7%,Si02 of 20%.The ULCB wire was developed by strengthening elements(Mn,Ni,Mo)and improving plasticity elements(Re,B,Ti).The microstructure of ULCB steel welded seam mainly consists of acicular ferrite and granular bainite,the microstructure of HAZ is coarser,which leads to softening and embrittlement.The spherical inclusions are oxide and silicate in the deposited metal,which speeds up the development of micro-cracks and lead to the weld seam is a weak area of the joint.The tensile strength of the welded joint gets to 805 MPa,which is about 94.71%of the base metal.The impact energy at-10? is more than 110J,and the average of percent shear fracture appearance is up to 85%.When welding heat input is 17298 J/cm,a small amount of QF and PF in HAZ.When the welding heat input is 15577J/cm,the HAZ microstructure for the QF and GB.The microstructure is BF and GB for 14790 J/cm.The impact energy and the shear area of welding joints are decreased with the increase of heat input.The tensile strength of welded joints is closely related with the carbon equivalent and the content of acicular ferrite.The impact energy of the joint is mainly affected by the carbon equivalent of welding wire and welding heat input.